There is available a resolver disclosed in JP 5524600 B as a detection device for detecting rotation, using a decelerator and a plurality of resolvers.
FIG. 4 is a cross sectional view of a conventional encoder disclosed in JP 5524600 B in a direction perpendicular to the shaft direction thereof. FIG. 5 is a cross sectional view along line B-B shown in FIG. 4. FIG. 6 is a cross sectional view along line A-A shown in FIG. 4. A rotor 60 is assembled to an input shaft 19 and rotates once as the input shaft 19 rotates once. Also, a gear 25, also assembled to the input shaft 19, is engaged with a gear 26 and drives a shaft 20 and a gear 27. The gear 27 is engaged with brass gears 28, 30 and drives respective rotors 62, 64. When the gears are assembled as described above to thereby constitute a deceleration mechanism, the rotor 62 rotates once as the input shaft 19 rotates twenty-four times, and the rotor 64 rotates once as the input shaft 19 rotates twenty-five times. FIG. 3 is a cross sectional view of a resolver, showing in an enlarged manner a left side resolver portion shown in FIG. 6 upside down. Each of the brass gears 28, 30 has a hole formed at the center thereof through which a respective metal bearing 93, 94 passes. Each of the brass gears 28, 30 is formed through lathe machining and subsequent hobbing machining with respect to the outer diameter portion thereof. Also, when the brass gears 28, 30 and the metal bearings 93, 94 are adhered and assembled such that stationary shafts 12, 13 are inserted into holes formed on the respective metal bearings 93, 94, and the outside wheels of the respective metal bearings 93, 94 are inserted into holes formed on the respective brass gears 28, 30, movement of the brass gears 28, 30 in the radial direction and the thrust direction is restricted. Also, the brass gears 28, 30 are engaged with the gear 27, and rotate at a predetermined reduction ratio relative to the input shaft. Each of the stationary shafts 12, 13 is made of metal material such as steel and pushed into an aluminum casing 81, and fixed therein. Each of the rotor cores 62, 64 has a deflected outer shape, and is made of soft magnetic material, such as ferrite, electromagnetic stainless, or silicon steel plate, and adhered and fixed to the outside wheel of the respective metal bearing 93, 94 and the respective brass gear 28, 30.
A stator portion 66 has four salient poles 101, 102, 103, 104 formed thereon. These four salient poles are arranged along the outer circumference of the rotor core 62 concentrically with the rotation center of the rotor 62. Around each of the salient poles, a two-phase detection wiring 16 and an excitation wiring 17 are arranged such that magnetic resistance will change as the air gap between the rotor core 62 and the tip end of the salient pole of the stator portion 66 changes as the rotor core 62 rotates. This change causes the induced voltage of the two-phase detection wiring 16 to change, which enables detection of the rotation position of the rotor core 62. A rotation position of the rotor core 64 also can be detected in a similar manner.
Use of the bearings 93, 94, such as a ball bearing etc., for receiving a radial load and a thrust load with the resolver rotation shaft shown in FIG. 6 increases costs. Also, although use of resin for the brass gears 28, 30 and a housing can reduce costs and ensure small variation of backlash due to change in temperature, use of resin for the thrust bearing results in a problem of increasing the amount of abrasion of the bearing.